Light-emitting element and display device

ABSTRACT

A phosphor element includes a pair of electrodes opposed to each other and a phosphor layer sandwiched between the pair of electrodes and having silicon fine particles whose average particle diameter is not more than 100 nm, and at least a part of a surface of the silicon fine particle is covered with a conductive material. In addition, the conductive material may include an oxide or a composite oxide containing at least one element selected from a group of indium, tin, zinc, and gallium.

TECHNICAL FIELD

The present invention relates to a phosphor element including a phosphorinorganic material and a display device using the phosphor element.

BACKGROUND ART

There is a display device using an electro luminescent (hereinafterreferred to as EL) element, as a display device in a flat panel displaywhich has been focused on together with a liquid crystal panel, a plasmadisplay and the like. The EL element includes an inorganic EL elementusing an inorganic compound as a light emitter and an organic EL elementusing an organic compound as the light emitter. The EL element hashigh-speed response, high contrast, vibration resistance and the like.Since the EL element has no gas in itself, it can be used under high orlow pressure.

According to the EL element, although certain gradient can beimplemented by driving in an active matrix method using a thin filmtransistor (TFT) because its driving voltage is low, the element iseasily influenced by moisture and the like, so that it has a short life.In addition, the inorganic EL element is characterized in that it has along life, a wide operating temperature range and excellent decaydurability as compared with the organic EL element. Meanwhile, since avoltage required to emit light in the inorganic EL element is as high as200V to 300V in general, it is difficult to drive it in the activematrix method using the thin film transistor (TFT). Therefore, theinorganic EL element has been driven by a passive matrix method.

According to the passive matrix driving, a plurality of scan electrodesextending parallel to a first direction and a plurality data electrodesextending parallel to a second direction which is perpendicular to thefirst direction are provided, a phosphor element is sandwiched betweenthe scan electrode and the data electrode which intersect with eachother, and one phosphor element is driven when an AC voltage is appliedbetween the pair of scan electrode and data electrode. Since averageluminance becomes low as a whole of the display device as the number ofthe scanning lines is increased in the passive matrix driving, it isnecessary to improve the luminance as the phosphor element. In addition,the inorganic light emitter is provided by doping a phosphor material inan insulator crystal in general and it emits light when UV light isirradiated, but even when an electric field is applied, electrons arenot likely to be spread and reaction against charging is strong, so thata high-energy electron is needed to emit light. Therefore, it isnecessary to take measures to emit light with low-energy electrons.

According to the technique described in Japanese Patent Publication No.54-8080, Mn, Cr, Tb, Eu, Tm, Yb or the like is doped in a phosphor layerincluding ZnS mainly to drive (flash) an inorganic EL element, so thatemission luminance can be improved, but since it can be driven at highvoltage of 200V to 300V only, the TFT cannot be used.

In addition, Japanese Patent Laid-open Publication No. 8-307011discloses a phosphor element using silicon fine particles. According tothe phosphor element, since a size of the silicon fine particle is verysmall such as 50 nm, a quantum effect is generated and a band gap widthbecomes a visible light region. Thus, the light is emitted in thevisible light region.

SUMMARY OF THE INVENTION

When the phosphor element is used as a high-quality display device in atelevision and the like, it is necessary to drive the phosphor elementat a low voltage so that the TFT can be used.

It is an object of the present invention to provide a phosphor elementwhich can be driven at a low voltage and can use a thin film transistor.

A phosphor element according to the present invention includes a pair ofelectrodes opposed to each other, a phosphor layer sandwiched betweenthe pair of electrodes and having silicon fine particles whose averageparticle diameter is not more than 100 nm. Then, at least a part of asurface of the silicon fine particle is covered with a conductivematerial.

When an external electric field is applied to the phosphor layer andelectrons are spread in silicon fine particles, silicon emits light by aquantum effect. In this case, the inventor of the present inventionfound that when a surface of the silicon fine particle having a particlediameter of 100 nm or less was covered with a conductive material, theelectrons could be easily spread in the silicon fine particles and lightwas emitted at a low voltage.

Each component of the phosphor element according to the presentinvention will be described.

The phosphor element may be fixed onto a substrate. The substrate isformed of a material having high electric insulation. When light of thephosphor element is emitted from the substrate side, the substrate isformed of a material having high optical transparency in a visibleregion. When a temperature of the substrate reaches several hundred of °C. at a manufacturing step of the phosphor element, a material which hasa high softening point, excellent heat resistance and thermal expansioncoefficient which is almost the same as that of a laminated layer is tobe used. Although glass, ceramics, a silicon wafer may be used in suchsubstrate, non-alkali glass may be used so that alkali ion and the likecontained in normal glass may not affect the phosphor element. Inaddition, alumina and the like may be coated on a glass surface as anion barrier layer of alkali ion for the phosphor element.

The electrode is formed of a material in which an electric conductionproperty is high and there is no migration of ion by the electric field.For example, aluminum, molybdenum, tungsten may be used for theelectrode. Since the electrode of the phosphor element on the phosphorside may be formed of a material having high transparency in the visibleregion in addition to the above performance, an electrode mainly formedof tin doped indium oxide (ITO) and the like can be used for the aboveelectrode. In addition, when both of the pair of electrodes aretransparent electrodes, both-side phosphor element can be provided.Furthermore, the phosphor element and the display device according tothe present invention may be driven by a DC current, an AC current or apulse.

For the conductive material, conductive inorganic material which istransparent in the visible region can be used. It is preferable that theconductive material includes an oxide or a composite oxide containing atleast one element selected from a group of indium, tin, zinc, andgallium. The oxide material may include Ga₂O₃, GaInO₃, In₂O₃, SnO₂,In₄Sn₃O₁₂, ZnO, CdIn₂O₄, Cd₂SnO₂, Zn₂SnO₄, MgIn₂O₄, ZnGa₂O₄, CdGa₂O₄,CaGa₂O₄, AgInO₂, InGaMgO₄, InGaZnO₄, and the like. In addition, asanother example, it is preferable that the conductive material includesa nitride (for example, titanium nitride) or a composite nitridecontaining at least one element selected from a group of titanium,zirconium, hafnium, gallium, and aluminum. As still another example, athin film of metal such as gold, silver, platinum, copper, rhodium,palladium, aluminum, chrome and the like or an alloy containing mainlythe above (magnesium silver alloy, for example) may be used. Inaddition, the silicon fine particles having the conductive material onat least one part of its surface may be dispersed in a transparentconductor matrix material. The transparent conductor matrix materialpreferably includes polyacetylene series; polyphenylene series such aspolyparaphenylene, polyphenylenevinylene, poliphenylenesulfide,polyphenyleneoxide; heterocyclic polymer series such as polypyrrole,polythiophene, polyfurane, polyselenophene, polytellurophene; ionicpolymer series such as polyaniline; polyacene series; polyester series;metal phthalocyanine series, these derivative, copolymer and mixture,and the like. As a more preferable example, there arepoly-N-vinylcarbozole (PVK), polyethylenedioxythiophene (PEDOT),polystyrenesulfonate (PPS), polymethylphenylsilane (PMPS) and the like.Furthermore, a polymer having electron transport property which will bedescribed in detail below may be used. Still furthermore, its electroconductivity may be adjusted by dispersing low-molecular organicmaterial having the electron transport property, or conductive orsemi-conductive inorganic material, in the conductive or semi-conductivepolymer.

An electron transport layer formed of the material including theelectron transport property may be formed between the electrode and thephosphor layer. The material including the electron transport propertyis a material having high electron mobility, which can promptlytransport electrons in the electron transport layer. In a case of theorganic material, a material mainly including aluminum quinolinate oroxadiazole derivative may be used, and in a case of the inorganicmaterial, a single-crystalline body, polycrystalline body of an n-typesemiconductor material and a resin diffused layer and the like of itsparticle powder can be used.

An electron hole transport layer formed of a material having electronhole transport property may be formed between the electrode and thephosphor layer. The electron hole transport layer may be providedbetween the electrode serving as a positive electrode and the phosphorlayer. The material having the electron hole transport property is amaterial having high electron hole mobility, which promptly transportsthe electron hole in the electron hole transport layer, and a materialmainly including polyvinyl carbozole series or polyphenylenevinyleneseries may be used.

A constitution of the phosphor element according to the presentinvention will be described.

As shown in FIG. 1, the phosphor element includes a phosphor layercontaining silicon fine particles having at least one part of thesurface covered with the conductive material as the light emitter,between the pair of electrodes opposed to each other. That is, thephosphor element has a fundamental constitution in which the phosphorlayer is sandwiched between the pair of electrodes and each electrode isconnected to a power supply. In addition, the electrode may be formed onthe substrate. Furthermore, the silicon fine particles having a surfacecovered with the conductive material may be dispersed in the transparentconductor matrix. In addition, the electron transport layer may beprovided between the electrode and the phosphor layer. Furthermore, anelectron injection layer may be provided between the electron transportlayer and the electrode. In addition, the electron hole transport layermay be provided between the electrode serving as the positive electrodeand the phosphor layer. Still furthermore, the electron hole injectionlayer may be provided between the electron hole transport layer and thepositive electrode. Since the phosphor element is driven at the lowvoltage, when the thin film transistor (TFT) is provided in thestructure, the display can implement active matrix driving at the lowvoltage.

Next, a condition to provide sufficient emission efficiency in thephosphor element will be discussed. The phosphor element is driven whenthe external electric field is applied to the electrode of the phosphorelement, and the electrons are transported to the light emitter in thephosphor layer by the applied external electric field. Since the siliconfine particles having a size of 100 nm or less are provided in thecenter of the light emitter, when the electrons are spread in the centerof the light emitter, silicon is excited by the quantum effect to emitlight. Since the surface of the silicon fine particle is covered withthe conductive material, the electrons are easily spread in the siliconfine particles of the center.

Here, the silicon fine particles are excited by transmitted electronenergy, and then, the silicon fine particle emits light when it ischanged from excited state to ground state. That is, as the particlediameter of the silicon fine particle becomes small, the quantum effectis more provided to enlarge the band gap. Thus, although the siliconfine particle having a particle diameter 100 nm or less emits light in avisible light region, as the particle diameter becomes small, itssurface area is increased and the particles become unstable. Therefore,it is necessary to cover the silicon fine particle surface in order tokeep the small particle diameter stably. In this case, it is preferablethat the surface of the silicon fine particle is covered with theconductive material. Thus, energy can be effectively transmitted to thesilicon atoms in the silicon fine particles.

In addition, when the electron transport layer is provided on thephosphor layer, the electrons can be effectively transmitted to thesilicon fine particle. Furthermore, when the phosphor layer issandwiched between the two electron transport layers formed of thematerial having the electron transport property, since the materialserves as an electron hole stopper also, the transmitted electrons arenot connected to the electron hole again, and the electrons can beeffectively transmitted to the silicon fine particles.

According to the phosphor element of the present invention, at least onepart of the surface of the silicon fine particle is covered with theconductive material, and the silicon fine particles are used as thelight emitters. Thus, light can be emitted in the visible light regionby the quantum effect and it can be chemically stabled. In addition, thephosphor element can be driven at the low voltage and the light can beemitted with high efficiency by the silicon fine particles.

BRIEF DESCRIPTION OF DRAWINGS

These objects and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings:

FIG. 1 is a sectional view showing a constitution of a phosphor elementaccording to a first embodiment of the present invention;

FIG. 2 is a sectional view showing a constitution of a phosphor elementaccording to an eighth embodiment of the present invention;

FIG. 3 is a perspective view showing an electrode constitution of aphosphor element according to a ninth embodiment of the presentinvention;

FIG. 4 is a schematic plain view showing a display device according to atenth embodiment of the present invention;

FIG. 5 is a sectional view showing another constitution of a phosphorelement according to a fourth embodiment of the present invention; and

FIG. 6 is a sectional view showing another constitution of a phosphorelement according to an eighth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although a phosphor element according to embodiments of the presentinvention will be described in detail with reference to the accompanyingdrawings hereinafter, the present invention is not limited to theembodiments. In addition, the same reference numerals are allotted tosubstantially the same components in the drawings.

First Embodiment

A phosphor element according to a first embodiment of the presentinvention will be described with reference to FIG. 1. FIG. 1 is aschematic view showing an element structure of the phosphor element 10.The phosphor element 10 has a phosphor layer 3 sandwiched between twofirst and second electrodes 2 and 4. According to a laminated relationof each layer, a transparent board 1 is provided as a substrate, and thefirst electrode 2, the phosphor layer 3 and the second electrode 4 arelaminated in this order thereon in the phosphor element 10. In addition,light is emitted from the side of the transparent board 1.

In addition, in the phosphor element 10, although a luminescent coloremitted from the phosphor element is determined by silicon fineparticles which constitute the phosphor layer 3, a color conversionlayer may be provided ahead of the phosphor direction of the phosphorlayer 3 or a color conversion material may be mixed in a transparentconductor matrix in order to display multiple colors, or white color orto adjust color purity of each color and the like. Since the colorconversion layer and the color conversion material may only have to emitlight as an excitation source, it may be an organic material or aninorganic material, so that a well-known fluorescent material, apigment, a dye and the like can be used. For example, when the colorconversion layer which emits light in complementary color to that of thelight from the phosphor layer 3 is provided, a surface light sourcewhich emits white light can be provided.

The luminescent characteristics of the phosphor element 10 will bedescribed. Extracting electrodes from the ITO transparent electrode(first electrode) 2 and the Ag electrode (second electrode) 4, then,applying an external voltage between the ITO transparent electrode 2 andthe Ag electrode 4 causes the phosphor element 10 to be emitted. Inaddition, according to the phosphor element in the first embodiment, asilicon fine particle surface having a particle diameter of 10 to 30 nmis covered with a titanium nitride film having a thickness of 10 to 30nm. Next, a manufacturing method of the phosphor element 10 will bedescribed. The phosphor element was manufactured according to thefollowing procedures.

-   (a) A non-alkali glass substrate was used as the substrate 1. A    thickness of the substrate 1 was 1.7 mm.-   (b) The ITO transparent electrode 2 was formed on the substrate 1    using an ITO oxide target as the first electrode 2 by a RF magnetron    sputtering method.-   (c) The phosphor layer 3 in which the silicon fine particle 5 was    covered with a conductive material 6 was formed on the ITO    transparent electrode 2 by an evaporation method.-   (d) The Ag electrode paste was screen-printed on the phosphor    element 3 as the second electrode 4 and dried to form the second    electrode 4.

According to the above steps, the phosphor element 10 was formed.

When the first electrode 2 and the second electrode 4 of the phosphorelement 10 were connected to a positive electrode and a negativeelectrode of a DC power supply 7, respectively and a DC voltage wasapplied to them, bright emission at 4.5V was confirmed. Since thephosphor element 10 can be driven at a low voltage, a pixel can becontrolled by the TFT

Second Embodiment

A phosphor element according to a second embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element 10 according to the first embodiment other than that aparticle diameter of a silicon fine particle 5 is different. Theparticle diameter of the silicon fine particle 5 was 5 to 20 nm.

When a first electrode 2 and a second electrode 4 of the phosphorelement according to the second embodiment were connected to a positiveelectrode and a negative electrode of a DC power supply 7, respectivelyand a DC voltage was applied to them, bright emission at 3.6V wasconfirmed. Since the phosphor element according to the second embodimentcan be driven at a low voltage, a pixel can be controlled by the TFT.

Third Embodiment

A phosphor element according to a third embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element 10 according to the first embodiment other than that aparticle diameter of a silicon fine particle 5 is different. Theparticle diameter of the silicon fine particle 5 was 70 to 100 nm. Whena first electrode 2 and a second electrode 4 of the phosphor elementaccording to the third embodiment were connected to a positive electrodeand a negative electrode of a DC power supply 7, respectively and a DCvoltage was applied to them, bright emission at 22V was confirmed. Sincethe phosphor element according to the third embodiment can be driven ata low voltage, a pixel can be controlled by the TFT

Fourth Embodiment

A phosphor element according to a fourth embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element 10 according to the first embodiment other than that aconductive material 6 is a magnesium silver alloy. A molecule ratio ofmagnesium and silver was 10:1 and a film thickness was 5 to 50 nm. Whena first electrode 2 and a second electrode 4 of the phosphor elementaccording to the fourth embodiment were connected to a positiveelectrode and a negative electrode of a DC power supply 7, respectivelyand a DC voltage was applied to them, bright emission at 3.1V wasconfirmed. Since the phosphor element according to the fourth embodimentcan be driven at a low voltage, a pixel can be controlled by the TFT.

In addition, when a metal material is used instead of a semiconductormaterial as the conductive material which covers the silicon fineparticles, it is preferable that not entire surface of the silicon fineparticle but only a part of thereof is covered with the conductivematerial. In this case, as shown in FIG. 5, the phosphor layer 3 may beconstituted by diffusing such silicon fine particles 15 in which a partof the surface is covered with a conductive material 16 formed of themetal material in a transparent conductor matrix 17 formed of asemiconductor material.

Fifth Embodiment

A phosphor element according to a fifth embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element according to the fourth embodiment other than that aparticle diameter of a silicon fine particle 5 is different. Theparticle diameter of the silicon fine particle 5 was 70 to 100 nm. Whena first electrode 2 and a second electrode 4 of the phosphor elementaccording to the fifth embodiment were connected to a positive electrodeand a negative electrode of a DC power supply 7, respectively and a DCvoltage was applied to them, bright emission at 19V was confirmed. Sincethe phosphor element according to the fifth embodiment can be driven ata low voltage, a pixel can be controlled by the TFT.

Sixth Embodiment

A phosphor element according to a sixth embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element according to the third embodiment other than that aconductive material 6 is mainly formed of Ga₂0₃. A particle diameter ofa silicon fine particle 5 was 70 to 100 nm. When a first electrode 2 anda second electrode 4 of the phosphor element according to the sixthembodiment were connected to a positive electrode and a negativeelectrode of a DC power supply 7, respectively and a DC voltage wasapplied to them, bright emission at 21V was confirmed. Since thephosphor element according to the sixth embodiment can be driven at alow voltage, a pixel can be controlled by the TFT

Seventh Embodiment

A phosphor element according to an seventh embodiment of the presentinvention will be described. This phosphor element is the same as thephosphor element according to the sixth embodiment other than that aconductive material 6 is mainly formed of In₄Sn₃O₁₂. A particle diameterof a silicon fine particle 5 was 70 to 100 nm. When a first electrode 2and a second electrode 4 of the phosphor element according to theseventh embodiment were connected to a positive electrode and a negativeelectrode of a DC power supply 7, respectively and a DC voltage wasapplied to them, bright emission at 16V was confirmed. Since thephosphor element according to the seventh embodiment can be driven at alow voltage, a pixel can be controlled by the TFT.

In addition, in the phosphor element according to the second embodimentto seventh embodiment, although a luminescent color is determined bysilicon fine particles 5 which constitute the phosphor layer 3, a colorconversion layer may be provided ahead of the phosphor direction of thephosphor layer 3 or a color conversion material may be mixed in thetransparent conductor matrix in order to display multiple colors, or awhite color or to adjust color purity of each color similar to the firstembodiment.

Eighth Embodiment

A phosphor element according to an eighth embodiment of the presentinvention will be described with reference to FIG. 2. FIG. 2 is asectional view showing a constitution of a phosphor element 20. Thephosphor element 20 is different from that in the first embodiment toseventh embodiment in that a first electron transport layer 8 isprovided between a phosphor layer 3 and a first electrode 2, and asecond electron transport layer 9 is provided between the phosphor layer3 and a second electrode 4. Electrons can flow into the phosphor layer 3well because of these electron transport layers 8 and 9. In addition,when the first electrode 2 and the second electrode 4 of the phosphorelement according to the eighth embodiment are connected to a positiveelectrode and a negative electrode of a DC power supply 7, respectively,the first electron transport layer 8 provided on the side of the firstelectrode 2 functions as an electron hole stopper layer. As a materialconstituting the electron transport layers 8 and 9, there are two maintypes of an organic material such as a low-molecular material and ahigh-molecular material.

The low-molecular material including an electron transport propertyincludes an oxadiazole derivative, a triazole derivative, astyrylbenzene derivative, a silole derivative, 1,10-phenanthrolinederivative, a quinolinol series metal complex, a thiophene derivative, afluorene derivative, a quinone derivative, and the like or their dimeror trimer. More preferably, although the following material may be used,the present invention is not limited to these, that is,2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD);2,5-biss(1-naphtyl)-1,3,4-oxadiazole (BND);2,5-bis[1-(3-methoxy)-phenyl]-1,3,4-oxadiazole (BMD);1,3,5-tris[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (TPOB);3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ);3-(4-biphenyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(p-EtTAZ);4,7-diphenyl-1,10-phenanthroline (BPhen);2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP);3,5-dimethl-3′,5′-di-tert-butyl-4,4′-diphenoquinone (MBDQ);2,5-bis[2-(5-tert-butylbenzoxazolyl)]-thiophene (BBOT);trynitrofluorenone (TNF); tris(8-quinolinolato) aluminum (Alq3); and5,5′-bis(dimesitylboryl)-2,2′bithiophene (BMB-2T) and the like.

In addition, the high-molecular material including the electrontransport property includespoly-[2-methoxy-5-(2-etyhlhexyloxy)-1,4-(1-cyanovinylene) phenylene](CN-PPV), polyquinoxaline, and a low-molecule polymer and the likeincorporating a molecular structure which shows the electron transportproperty, in a molecular chain. Furthermore, molecules of the abovelow-molecular material may be diffused in a conductive or non-conductivepolymer. In addition, a single-crystalline body of an n-typesemiconductor material in which electrons can be well injected and thereis no absorption in a visible light range as represented by zinc oxide(ZnO), indium oxide (In₂O₃), titanium oxide (TiO₂) and the like, itspolycrystalline body, or a resin diffused layer of its particle powderand the like may be used.

In addition, when the metal material is used as the conductive materialwhich covers the silicon fine particles instead of the semiconductormaterial, it is preferable that not entire surface of the silicon fineparticle but only a part thereof is covered with the conductivematerial. In this case, as shown in FIG. 6, the phosphor layer 3 may beconstituted by diffusing such silicon fine particles 15 in which onepart of the surface is covered with a conductive material 16 formed of ametal material, in a transparent conductor matrix 17 formed of asemiconductor material.

Ninth Embodiment

A phosphor element 30 according to a ninth embodiment of the presentinvention will be described with reference to FIG. 3. FIG. 3 is aperspective view showing an electrode constitution of the phosphorelement 30. The phosphor element 30 further includes a thin filmtransistor 11 connected to the electrode 2 of the phosphor elementaccording to the first embodiment to eighth embodiment. An x electrode12 and a y electrode 13 are connected to the thin film transistor 11.According to the phosphor element 30, since at least a part of a surfaceof a silicon fine particle 5 is covered with a conductive material 6, itcan be driven at a low voltage and the thin film transistor 11 can beused. In addition, when the thin film transistor 11 is used, thephosphor element 30 has a memory function. As this thin film transistor11, low-temperature polysilicon or amorphous silicon thin filmtransistor and the like may be used. Furthermore, it may be an organicthin film transistor constituted by a thin film including an organicmaterial, or may be a transparent thin film transistor formed of zincoxide and the like.

Tenth Embodiment

A display device according to a tenth embodiment of the presentinvention will be described with reference to FIG. 4. FIG. 4 is aschematic plain view showing an active matrix of the display device 40which is constituted by x electrodes 12 and y electrodes 13 intersectingwith each other. The display device 40 is an active matrix displaydevice having a thin film transistor 11. The active matrix displaydevice 40 includes a two-dimensional phosphor element array in which aplurality of phosphor elements 30 including the thin film transistors 11shown in FIG. 3 are arranged, the plurality of x electrodes extendingparallel to each other in a first direction which is parallel to asurface of the phosphor element array, and the plurality of y electrodes13 extending parallel to each other in a second direction whichintersects with the first direction at right angles. The thin filmtransistor 11 in the phosphor element connects the x electrode 12 to they electrode 13. The phosphor element specified by the pair of xelectrode 12 and y electrode 13 becomes a pixel. According to the activematrix display device 40, as described above, a phosphor layer 3constituting the phosphor element of each pixel includes silicon fineparticles 5 in which at least a part of its surface is covered with aconductive material 6. Thus, since it can be driven at a low voltage,the thin film transistor 11 can be used and a memory effect can beprovided. In addition, since it can be driven at the low voltage, thedisplay device has a long life. In addition, when the silicon fineparticles 5 constituting the phosphor layer 3 are arranged in each pixeldepending on its luminescent color (RGB), there can be provided afull-color display device using the three primary colors. In addition, acolor filter may be provided ahead of the phosphor direction in order toadjust the color purity of each color of RGB. Furthermore, the phosphorlayer 3 emitting one color to every pixel may be used, and a colorconversion layer and the color filter may be further provided ahead ofthe phosphor direction. Thus, when the color conversion layer absorbsblue light generated from the phosphor layer 3, green or red light isgenerated and when they are taken out respectively, there can beprovided a full-color display device using the three primary colorsaccording to another example.

COMPARATIVE EXAMPLE 1

A phosphor element according to a comparative example will be described.This phosphor element is the same as the phosphor element 10 accordingto the first embodiment other than that a particle diameter of a siliconfine particle is different and there is no conductive material on asurface. A particle diameter of a silicon fine particle in thecomparative example 1 was 180 to 220 nm. When a first electrode 2 and asecond electrode 4 of the phosphor element according to comparativeexample 1 were connected to a positive electrode and a negativeelectrode, respectively and a DC voltage was applied to them, brightemission at 103V was confirmed. Since the phosphor element according tothe comparative example 1 is driven at a high voltage, it is difficultor impossible to control a pixel by the TFT

COMPARATIVE EXAMPLE 2

A phosphor element according to a comparative example 2 will bedescribed. This phosphor element is the same as the phosphor element 10according to the first embodiment other than that a particle diameter ofa silicon fine particle is different. A particle diameter of a siliconfine particle in the comparative example 2 was 200 to 240 nm. Although afirst electrode 2 and a second electrode 4 of the phosphor elementaccording to the comparative example 2 were connected to a positiveelectrode and a negative electrode, respectively and a DC voltage wasapplied to them, emission could not be confirmed even at 200V

COMPARATIVE EXAMPLE 3

A phosphor element according to a comparative example 3 will bedescribed. This phosphor element is the same as the phosphor elementaccording to the fourth embodiment other than there is no conductivematerial. Although a first electrode 2 and a second electrode 4 of thephosphor element according to the comparative example 3 were connectedto a positive electrode and a negative electrode, respectively and a DCvoltage was applied to them, emission could not be confirmed even at200V.

COMPARATIVE EXAMPLE 4

A phosphor element according to a comparative example 4 will bedescribed. This phosphor element is the same as the phosphor elementaccording to the fourth embodiment other than a film thickness of amagnesium silver alloy is different and the film thickness is 60 to 100nm. Although a first electrode 2 and a second electrode 4 of thephosphor element according to the comparative example 4 were connectedto a positive electrode and a negative electrode, respectively and a DCvoltage was applied to them, emission could not be confirmed even at200V

COMPARATIVE EXAMPLE 5

A phosphor element according to a comparative example 5 will bedescribed. This phosphor element is the same as the phosphor element 10according to the first embodiment other than a film thickness oftitanium nitride which is the conductive material is different and thefilm thickness is 40 to 80 nm. Although a first electrode 2 and a secondelectrode 4 of the phosphor element according to the comparative example5 were connected to a positive electrode and a negative electrode,respectively and a DC voltage was applied to them, emission could not beconfirmed even at 200V.

As described above, although the present invention has been described indetail by the preferred embodiments, the present invention is notlimited to the embodiments, and as will be understood by those skilledin the art, many preferred variations and modifications can be made in atechnical scope of the present invention described in the followingclaims.

1. A phosphor element comprising: a pair of electrodes opposed to eachother; and a phosphor layer sandwiched between the pair of electrodesand having silicon fine particles whose average particle diameter is notmore than 100 nm, wherein at least a part of a surface of the siliconfine particle is covered with a conductive material.
 2. The phosphorelement according to claim 1, wherein the conductive material comprisesan oxide or a composite oxide containing at least one element selectedfrom a group of indium, tin, zinc, and gallium.
 3. The phosphor elementaccording to claim 1, wherein the conductive material comprises anitride or a composite nitride containing at least one element selectedfrom a group of titanium, zirconium, hafnium, gallium, and aluminum. 4.The phosphor element according to claim 1, wherein the conductivematerial is titanium nitride whose thickness is not more than 30 nm. 5.The phosphor element according to claim 1, wherein the conductivematerial is magnesium silver alloy whose thickness is not more than 50nm.
 6. The phosphor element according to claim 1, further comprising anelectron transport layer between the phosphor layer and at least one ofthe electrodes.
 7. The phosphor element according to claim 1, furthercomprising a thin film transistor connected to at least one of theelectrodes.
 8. A display device comprising: a two-dimensional phosphorelement array in which the phosphor elements are arranged, each phosphorelement comprising: a pair of electrodes opposed to each other; aphosphor layer sandwiched between the pair of electrodes and havingsilicon fine particles whose average particle diameter is not more than100 nm, wherein at least a part of a surface of the silicon fineparticle is covered with a conductive material; and a thin filmtransistor connected to at least one of the electrodes; a plurality of xelectrodes extending parallel to each other in a first direction whichis parallel to a surface of the phosphor element array; and a pluralityof y electrodes extending parallel to each other in a second directionwhich is perpendicular to the surface of the phosphor element array, andwherein the thin film transistor of the phosphor element array connectsthe x electrode to the y electrode.